The present invention relates to an optical pickup capable of scanning multiple tracks simultaneously, and more particularly, to an optical pickup for recording and/or reproducing information simultaneously on/from a plurality of tracks of a recording medium, which can be one of two thicknesses.
FIG. 1 is a diagram showing the optical arrangement of a general optical pickup.
As shown in FIG. 1, the optical pickup includes a light source 10, an objective lens 25, a beam splitter 23 and a photodetector 29. The optical source 10 includes a general edge emitting laser which emits light from the side of stacked semiconductor material layers. Referring to FIG. 2A, the edge emitting laser diode is attached to a side wall of a mount 12 fixed on a base 13 such that the light emitted from the side heads toward a recording medium 1 (see FIG. 1). As an alternative, as shown in FIG. 2B, the edge emitting laser diode 11 may be installed on a base 15, and a reflection mirror 14 for reflecting the light toward the beam splitter 23 (see FIG. 1) may be used.
The objective lens 25 of FIG. 1 converges the light from the light source 10 to focus a light spot on a recording surface of the recording medium 1.
The beam splitter 23 which is positioned on an optical path between the light source 10 and the objective lens 25 reflects most of the light from the light source 10 and transmits the light reflected from a recording surface of the recording medium 1 toward the photodetector 29.
The photodetector 29 receives the light reflected from the recording surface of the recording medium 1 to detect a radio frequency (RF) signal and an error signal. The photodetector 29 includes a plurality of divided plates (not shown) each receiving light independently.
Also, the optical pickup includes a grating 21 and a collimating lens (not shown) which are positioned between the light source 10 and the recording medium 1. The grating 21 diffracts the incident light into a 0-order beam and .+-.1st-order beams such that the photodetector 29 can detect a tracking error signal by a three-beam method. The collimating lens collimates a divergent beam.
Also, an astigmatism lens 27 may be further included on an optical path between the beam splitter 23 and the photodetector 29. Generally, the astigmatism lens 27 is semicylindrical in shape, and forms a circular beam on the photodetector 29 when the distance between the objective lens 25 and the recording medium 1 is in focus, and an oval beam on the photodetector 29 in other cases.
In the optical pickup having the above structure, information is recorded or reproduced while a single light beam emitted from the light source 10 travels spirally along tracks formed on the recording surface of the recording medium 1. Thus, the information processing speed of a recording/reproducing apparatus adopting the above optical pickup depends on the rotation speed of a spindle motor 5 rotating the recording medium 1. Thus, there is a limitation to increasing the rotation speed of the motor, and the stability of the system is lowered.